Plastic optical fibers have been used for transmitting optical signals, particularly for short span applications (e.g., 100 meters or less). They are advantaged over glass fibers in terms of easy handling, light weight and good ductility. POF are also easier to splice to each other and to the light source because of their large core diameter and high numerical. aperture. Furthermore, plastic optical fiber generally costs less in manufacturing than glass fibers.
Polymeric materials suitable for use as the core of plastic optical fibers must possess a set of stringent property requirements such as excellent transparency and low optical loss, good thermal stability, good chemical stability, and flexibility for bending, etc. In addition, polymers should be amendable to typical fiber spinning process for making optical fibers. Recent advances for various polymers investigated for POF can be found in a monograph entitled “Polymers for Lightwave and Integrated Optics”, Marcel Dekker, Inc (1992), by Lawrence A. Hornak. Traditionally, poly(methyl methacrylate) (PMMA) has been the primary choice of material for manufacturing the core of a plastic optical fiber. However, PMMA tends to absorb moisture that can deteriorate signal strength (or increase attenuation). Furthermore, PMMA does not provide adequate resistance to temperatures in excess of 85° C. At temperatures above 85° C., the optical loss in a PMMA plastic optical fiber will increase to an undesirable level.
Many applications require a plastic optical fiber with heat resistance to temperatures in excess of 85° C. and some applications, e.g., automotive, require heat resistance up to 125° C. A high heat performance POF is thus very desirable. There has been a considerable amount of research devoted to developing new optical materials other than PMMA that are suitable for plastic optical fiber use at temperatures in excess of 100° C. For example, U.S. Pat. No. 5,599,897 teaches high temperature plastic optical fiber compositions using aromatic polycarbonate. U.S. Pat. No. 4,798,445 teaches high temperature plastic optical fiber compositions using polycarbonate made with a melt spinning production process. U.S. Pat. No. 4,999,141 and EP 0,264,818 B1 teach high temperature plastic optical fiber compositions using silicone rubber and electron beam irradiation crosslinking process. EP 0,171,294 B1 teaches high temperature plastic optical fiber compositions using PMMA exposed to electron beam irradiation. U.S. Pat. No. 4,810,055 teaches high temperature plastic optical fiber compositions made from aliphatic N-substituted maleimide as a monomer unit and methyl methacrylate and/or styrene monomers. U.S. Pat. No. 7,512,309 teaches a polymer composition comprising 5 to 100% by mass of a unit (A) of a lactone compound and 0 to 95% by mass of a unit (B) of methacrylate as constitutional units for plastic optical fiber with good heat resistance and transparency.
Specifically, polycarbonate, amorphous cyclic olefin polymer (COP) or cyclic olefin copolymer (COC) and aliphatic N-substituted maleimide have been proposed for POF use. However, none of these materials can fully satisfy the performance requirements of POF. Polycarbonate, as taught in JP 06-200004, has large optical loss due to light scattering from non-uniformity in density and impurity in the polymer. COP or COC contain alicyclic groups in their main chain and show high heat resistance (JP 04-365003), but they also suffer issues such as difficulty in completely removing impurities. Further, cyclic olefin materials tend to be brittle and lack bending flexibility. As for aliphatic N-substituted maleimide such as described in U.S. Pat. No. 4,810,055, processing of the material into fiber is found to be challenging. Moreover, the approaches of polycarbonate and maleimide are potentially susceptible to moisture absorption which is detrimental for signal transmission.
U.S. Pat. No. 6,815,475 teaches compositions comprising a hydrogenated block copolymer have a multitude of uses including films, profiles, sheets, pultruded articles, fibers, coated articles, injection molded articles and blow or rotational molded articles. The compositions comprise a fully or substantially fully hydrogenated, rigid block copolymer that has at least two distinct blocks of hydrogenated, polymerized vinyl aromatic monomer and one block of hydrogenated, polymerized conjugated diene monomer. The hydrogenated diene block(s) and the hydrogenated vinyl aromatic blocks are present in a weight ratio of 40:60 or less.